1. The Field of the Invention
This invention relates to explosive devices employed to detonate explosive materials of the types used in mining and construction, and to explosive devices used in seismic survey activity. The present invention has particular applicability to explosive devices made of cast explosive materials.
2. Background Art
A. Types of Explosive Devices
Typically, two components are involved in initiating the detonation of an explosive device.
The first of these components is stimulated directly from a control device in order to initiate the explosion. Such components include detonators and transmission lines, such as detonating cords, shock tubes, and electrically conductive wires. In the former, a highly explosive material is concentrated in the small package at the end of a cable that is capable of communicating an electrical or another type of stimulus to the detonator from the detonation control device. A detonating cord, by contrast, is a continuous thread of highly explosive material. Once a stimulus for detonation is applied at the output end of a detonating cord remote from the detonator, the detonating cord detonates along the length thereof in a progressive manner. Shock tubes function in a similar manner. Conductive wires, by contrast, convey electrical current to the explosive device, thereby initiating the detonations of the explosive material of the explosive device.
The use of detonators and transmission lines permits safe, remote initiation of the explosion of explosive devices, but neither is of itself capable of generating adequate energy to produce a shock front suitable to the needs of mining, construction, or seismic survey activity. Therefore, a transmission line or a detonator is used to explode a larger explosive device that is generally made of a less sensitive explosive material than is the detonator or the detonating cord.
An explosive device thus functions to amplify the energy of a detonator, a shock tube, or a detonating cord into an explosion sizable enough to produce a shock wave front that effects useful work. In mining and construction activity, the work performed by the shock wave front is that of initiating the detonation of a relatively insensitive explosive material of large volume. In seismic survey activity, the work performed by the shock wave front is that of producing vibrations that travel through subsurface geological structures and are reflected from the interfaces between subsurface structures possessed of differing qualities. These reflected seismic shock wave fronts are detected remotely from the source of the seismic shock wave front and used in computer calculations to map the locations and extent of such subsurface interfaces between structures possessed of different qualities.
A typical configuration of the elements of a system that produces an explosive detonation used in mining and construction is shown in FIG. 1. There, a borehole 10 has been drilled to a predetermined depth into a subsurface geological formation 11, which is to be shattered by explosives, possibly to prepare it for subsequent mechanical removal. An explosive device, in this case an explosive booster device 12, has been lowered to the bottom 13 of borehole 10. By way of illustration, operably engaged within explosive booster device 12 is a detonator 14 at the output end of a transmission line, in this case a detonating tube 15. Detonating tube 15 leads to a selectively operable control device, in this case a detonating tube trigger box 16. With explosive booster device 12 and detonator 14 thus disposed at the bottom 13 of borehole 10, a suitable low energy, high volume explosive material 17 has been poured into borehole 10 contacting explosive booster device 12.
Trigger box 16 is a pedal operated device that ignites a quantity of gun powder comparable in amount to that in a shotgun shell. The gun powder is disposed at the output end of detonating tube 15 remote from detonator 14. The firing of the quantity of gunpowder in trigger box 16 commences a slow detonation that travels along detonating tube 15 from trigger box 16 to detonator 14. The arrival of this traveling detonation along detonating tube 15 at detonator 14 sets off detonator 14, which in turn leads to the explosion of explosive booster device 12. This explosion produces a shock wave front that travels radially outwardly from explosive booster device 12. A portion of that shock wave front, which is referred to as a detonating wave front, passes through high volume explosive material 17, causing the detonation thereof. The entire process is completed within a few milliseconds. In order to contain and drive laterally into geological formation 11 the explosive force of high volume explosive material 17, the open end 18 of borehole 10 has been stemmed with backfill 19.
Geological formation 11 in which borehole 10 was drilled and equipped for explosive detonation as shown in FIG. 1 could be located at the surface of the ground, at the bottom of a mining pit, or underground at the working face of a mine. Typically, an array of boreholes, such as borehole 10, is prepared together in a rock formation before any detonation occurs. Then, the columns of blasting agent in the borehole matrix are detonated simultaneously or in a nearly simultaneous pattern progression of detonations according to the specific consequences sought. The depth of borehole 10 and the height of the column of the high volume explosive material 17 placed therein are dictated by the nature of geological formation 11, as well as by the objective of the blasting exercise.
A typical configuration of the elements of a system that produces an explosive detonation used in seismic survey operations is shown in FIG. 2. There, a borehole 10 has been drilled a predetermined depth into a subsurface geological formation 11, through which a shock wave front is to be propagated for seismic survey purposes. The shock wave front is reflected off of the interfaces between subsurface structures of differing quality in geological formation 11. The reflected shock waves are then measured at an array of seismic detectors. The data from the seismic detectors for a number of shock wave fronts from different explosions is then processed to produce a three-dimensional map of the subsurface structures in geological formation 11.
An explosive device taking the form of explosive seismic device 20 has been lowered to the bottom 13 of borehole 10. Operably engaged within explosive seismic device 20 is a detonator 14 that communicates with a detonation control box 22 by way of a transmission line taking the form of an electrically conductive wire 21.
Detonation control box 22 is a hand-operated plunger device that generates an electrical signal that travels along wire 21 from detonation control box 22 to detonator 14. The arrival of this electrical signal at detonator 14 sets off the highly energetic explosive material of detonator 14. The energy from detonator 14 in turn causes the explosion of explosive seismic device 20.
The explosion of explosive seismic device 20 produces a shock wave front that travels radially outward from explosive seismic device 20, passing through geological formation 11 and being reflected off of subsurface structures therein possessed of differing qualities. The entire process, from activation of detonation control box 22 to the measurement of reflected shock waves at the seismic detectors, is completed in a few milliseconds. To contain the explosive force of explosive seismic device 20 and to drive the resulting shock wave front laterally into geological formation 11, borehole 10 has been stemmed with backfill 19. Although borehole 10 is illustrated in FIG. 2 as being completely stemmed with backfill 19, boreholes in seismic operations can also be partially stemmed with backfill.
FIG. 3 illustrates a typical configuration of the elements of a system that produces an explosive detonation used to create a seismic shock wave front from above the ground surface of a geological formation 11. An explosive seismic device 23 has been secured with a seismic survey rod 24 above the surface of the geological formation 11 to be seismically surveyed. By way of illustration, operably coupled between explosive seismic device 23 and a remotely operated detonation box 26 is a transmission line, in this case a detonating cord 25.
The remotely operated detonation box 26 illustrated in FIG. 3 is selectively controlled by radio frequency signals Rf emitted by a remote control 27. Upon receiving radio frequency signals Rf, an electric cap within detonation box 26 introduces an electrical current into a wire 21 extending a distance from detonation box 26, which in turn initiate explosion of a detonator 14 external of detonation box. Detonator 14 causes detonating cord 25 to detonate. The detonation travels along detonating cord 25 to explosive seismic device 23, thus effecting the detonation of the explosive material of explosive seismic device 23. As the explosive material of explosive seismic device 23 detonates, seismic survey rod 24 is driven into geological formation 11, transmitting a shock wave front generated by explosive seismic device 23 into geological formation 11. The shock wave front is then reflected by subsurface structures of differing quality in geological formation 11. The reflected shock waves are detected at an array of seismic detectors. The entire process, from sending radio frequency signals Rf from remote control 27 to the detection of reflected shock waves at the seismic detectors, is completed in a few milliseconds. Data generated by the array of seismic detectors upon measuring reflected shock waves from a number of explosions is used to generate a three-dimensional map of geological formation 11.
B. The Mechanics of Detonation
The manner in which a transmission line, such as detonating tube 15, or detonator 14 detonates an explosive device, such as explosive booster device 12, is illustrated in the sequence of FIGS. 4A-4E.
In FIG. 4A, a detonating impulse I travels along detonating tube 15 to detonator 14, exploding detonator 14. As detonator 14 explodes, a detonating wave front 28, shown in FIG. 4B, is created that travels radially outwardly through the explosive material of explosive booster device 12 from the position at which detonator 14 was located. As detonating wave front 28 passes through explosive material, the explosive material detonates.
FIG. 4B illustrates the manner in which detonating wave front 28 begins traveling through explosive booster device 12. Detonating wave front 28 continues traveling in a substantially radial fashion through explosive booster device 12, as shown in FIG. 4C, until detonating wave front 28 reaches the exterior of explosive booster device 12.
As depicted in FIG. 4D, when a portion of detonating wave front 28 has detonated all of the explosive material of explosive booster device 12 in the path of that portion of detonating wave front 28, that portion of detonating wave front 28 becomes a shock wave front 29.
Within a matter of milliseconds, all of the explosive material of explosive booster device 12 has been detonated as depicted in FIG. 4E. The shock wave front 29 from explosive booster device 12 effects the explosion of the high volume explosive material 17 depicted in FIG. 1 or creates seismic waves in the geological formation 11 illustrated in FIGS. 2 and 3.
C. Manufacture of Conventional Explosive Devices
Conventionally, explosive devices of the types described above are manufactured in open-topped molds having cavities of the desired configuration, such as prismatic, cylindrical, or frustoconical. Interior features of the explosive devices, such as passageways therethrough, are formed by solid inserts positioned in the open-topped mold. After solid inserts have been disposed in the open-topped mold, molten explosive material is poured manually or automatically into the cavity of the mold. As the explosive material cools, the explosive material solidifies to form a cast explosive device. The solid inserts are then removed from the explosive device to open up the passageways formed thereby. Thus, conventional methods for manufacturing explosive devices can be labor intensive and time consuming.
When cardboard molds are used, the cardboard molds may remain on the explosive devices in use thereof or can be removed from the explosive devices. Reusable molds can only be employed in the manufacture of explosive devices having prismatic configurations or configurations with transverse cross sections that taper progressively along the length of these explosive devices. Explosive devices that have transverse cross sections that do not taper progressively along the length thereof cannot be removed from an open-topped mold without destroying the mold. Moreover, explosive devices with internal cavities having complex shapes cannot be easily formed by conventional explosive material molding techniques.
No practical methods exist for manufacturing segmented explosive boosters, particularly explosive boosters that receive a detonator or a portion of a transmission line.
D. Explosive Devices Contrasted with Solid Rocket Motors
Pentolite is explosive material that is commonly used in explosive devices such as explosive booster devices and explosive seismic devices. A shock wave front will travel through Pentolite at a rate of about 7,400 to 7,600 meters per second, detonating the Pentolite at a rate of about 7,400 to 7,600 meters per second. Other explosive materials also detonate to cause an explosion.
Solid rocket motors are not configured to explode. Solid rocket motors are configured to burn at controlled rates. The burning of a rocket motor is not caused by a detonating wave front, but by igniting the propellant material of the solid rocket motor. After igniting the propellant material of a solid rocket motor, the propellant material simply burns at a predetermined rate until the propellant material is consumed. Thus, rocket motors do not detonate. The rate at which the materials of solid rocket motors burn is very slow relative to the rate at which explosive materials detonate.
Rockets are designed to transport cargo. Solid rocket motors are typically configured to burn evenly for an extended duration, generating large quantities of relatively low-velocity exhaust gases in the process. If the material of a rocket motor were to transition from a controlled burn to a state of detonation, the rocket motor would explode, destroying the rocket and the cargo to be carried thereby. Because of the uses for which rocket motors are designed and since solid rocket motors are configured to burn at controlled rates, rocket motors are different from explosive devices, such as the explosive devices illustrated in FIGS. 1-3. A rocket booster is most emphatically not an explosive booster.
It is thus a broad object of the present invention to increase the speed and efficiency with which explosive devices may be manufactured.
It is also an object of the present invention to permit the manufacture of explosive devices having configurations that cannot be readily manufactured by conventional processes.
It is a further object of the present invention to increase the velocity of detonation of explosive devices.
To achieve the foregoing objects, and in accordance with the invention as embodied and broadly described herein, segmented explosive devices, as well as systems and methods for manufacturing and using segmented explosive devices, are provided.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims.
In one form, an apparatus incorporating teachings of the present invention, which is capable of producing a shock wave front upon being exploded by a detonation signal generated by a selectively operable control device and communicated to the apparatus by a transmission line coupled between the control device and the apparatus, has an elongate explosive first charge segment and an elongate explosive second charge segment. First and second abutment surfaces are formed on the exterior surfaces of the first and second charge segments, respectively. The first charge segment has a cavity recessed in the first abutment surface thereof. The cavity is configured to receive the output end of the transmission line. The first abutment surface of the first charge segment is disposed against the second abutment surface of the second charge segment in an assembled relationship of the first and second charge segments. Assembly means secure the first and second charge segments in the assembled relationship thereof.
An example of the assembly means that is useful for securing the first and second explosive charge segments together in the assembled relationship thereof is an adhesive material disposed between the first and second abutment surfaces to secure the first charge segment to the second charge segment. Other assembly means may be disposed on an external surface of the explosive device to secure the first charge segment to the second charge segment in the assembled relationship thereof.
The first abutment surface can also include male-female mating means thereon. The male-female mating means are positioned to receive complimentarily configured and positioned female mating means and male mating means on the second abutment surface of the second charge segment. When the first and second charge segments are disposed in the assembled relationship thereof, the male-female mating means stabilize the disposition of the first charge segment and the second charge segment.
In one aspect of the present invention, the male mating means are nodules that protrude from one of the first and second abutment surfaces and the female mating means are recesses configured complimentarily to the nodules and positioned correspondingly to the nodules on the other of the abutment surfaces.
In another aspect of the present invention, the amount of time required to completely detonate an explosive device is decreased. As a shock wave front travels through voids in an explosive device, a plasma zone propagates ahead of the shock wave front. When the plasma zone impacts explosive material in the path thereof, plasma in the plasma zone causes the explosive material to detonate. Accordingly, the present invention includes a segmented explosive device having advancement means for permitting a plasma zone to progress internal of the explosive device and for initiating a secondary detonating wave front ahead of the initial detonating wave front. The advancement means thus facilitates advance detonation of the explosive device by providing one or more voids in which the plasma zone will travel and impact explosive material. The advancement means can be a non-linear channel recessed in the first abutment surface of the first charge segment. As a plasma travels through the non-linear channel in advance of a shock wave front, the plasma zone impacts explosive material of the explosive device at bends in the non-linear channel, initiating secondary detonation of the impacted explosive material and forming a secondary detonating wave front in the explosive material in the path of the plasma zone. Alternatively, the advancement means can be a cavity with a transverse cross section having a configuration or a size that changes along the length of the cavity. As a plasma zone travels through the cavity and impacts explosive material protruding into the channel in the path of the plasma zone, a secondary detonation is initiated and a secondary detonating wave front is created in the explosive material that protrudes into the path of the plasma zone.
According to yet another aspect of the invention, a charge segment can have two types of explosive materials. For example, the cavity recessed in the first abutment surface of the first charge segment is lined with a second explosive material that detonates with greater sensitivity than the first explosive material of the first charge segment.